As conventional materials of insertable and extractable connecting terminals, there are used tin-plated products wherein a tin plating film is formed as the outermost layer of a conductive material, such as copper or a copper alloy. In particular, tin-plated products are used as the materials of information communication equipment for automotive vehicles, portable telephones and personal computers, control substrates for industrial equipment, such as robots, terminals, such as connectors, lead frames, relays and switches, and bus bars, from the points of view of their small contact resistance, contact reliability, corrosion resistance, solderability, economy and so forth.
As a method for producing such a tin-plated product, there is proposed a method for producing a plated copper or copper alloy wherein a nickel or nickel alloy layer is formed on the surface of copper or a copper alloy, and a tin or tin alloy layer is formed on the outermost surface side thereof, at least one layer of intermediate layers containing copper and tin as main components or intermediate layers containing copper, nickel and tin as main components being formed between the nickel or nickel alloy layer and the tin or tin alloy layer, and at least one intermediate layer of these intermediate layers containing a layer which contains 50% by weight or less of copper and 20% by weight or less of nickel, the method comprising the steps of: forming a plating film of nickel or a nickel alloy having a thickness of 0.05 to 1.0 μm on the surface of copper or the copper alloy; forming a plating film of copper having a thickness of 0.03 to 1.0 μm thereon; forming a plating film of tin or a tin alloy having a thickness of 0.15 to 3.0 μm on the outermost surface; and then, carrying out a heating treatment at least once (see, e.g., Patent Document 1).
There is also proposed a conductive material for connecting parts, wherein a copper-tin alloy coating layer, which contains 20 to 70% by atom of copper and which has an average thickness of 0.2 to 3.0 μm, and a tin coating layer, which has an average thickness of 0.2 to 5.0 μm, are formed on the surface of a base material of a copper plate or bar in this order, and the surface thereof is reflow-treated, the arithmetic average roughness Ra in at least one direction being 0.15 μm or more, the arithmetic average roughness Ra in all directions being 3.0 μm or less, a part of the copper-tin alloy coating layer being exposed to the surface of the tin coating layer, and the exposed area ratio of the copper-tin alloy coating layer being 3 to 75% with respect to the surface of the conductive material (see, e.g., Patent Document 2).